This invention relates to rotary material processors and is generally related to processors of the screw conveyor type having conveying, mixing and heat exchange capabilities.
Material processors which function to convey, mix and act as a heat exchanger for fluid materials are well known. The term "fluid material" as used herein refers to any non-gaseous material which can be made to move within or through a screw type processor, and thus includes such diverse materials as liquids, slurries and particulates.
Such processors operate well for their intended purposes, but oftentimes are massive, complex in design and fabrication requirements, and difficult to repair. The requirement to alleviate thermal stresses and strains which occur during operation is a primary cause of design complexity. The processors, when circulating a heat exchange fluid through, for example, discs, tubes or hollow flights, should be highly reliable and free of leakage paths to avoid intermixing of the heat transfer medium and the medium being moved through or within the processor. Stresses are oftentimes induced during manufacture which complicate the maintenance of a high integrity system. Processors of this type often require large amounts of welding during fabrication which can complicate repair and particularly replacement of component parts.
Typically the processors are of two main types. The first utilizes hollow helical flights permanently mounted on a rotatable central shaft which functions to support the flights and direct a heat transfer medium into and out of the flights. These units can provide excellent conveying characteristics. The second type utilizes a singular hollow helical tube wrapped contiguously or spaced about a central rotatable shaft. Flow of a heat transfer medium through the helical tube and commonly the shaft can provide excellent heat transfer characteristics. Other types of mixers and conveyors are known, but are not as common. It is also well known to position two or more processors with hollow helical flights of various profiles in parallel such that the flights intermesh to provide a cleaning or wiping action for the adjacent shaft and conveyor flight assembly.
Exemplary of the first type is U.S. Pat. No. 3,529,661 which discloses hollow helical flights welded across the gaps of a pad wrapped in a helical fashion about a central shaft. This unit is extremely reliable and has found acceptance thoughout a variety of commercial applications. It does, however, require time consuming welding operations. U.S. Pat. No. 2,731,241 is also exemplary, and shows the wide variety of profiles useful as hollow flights, each affixed to a central shaft, particularly where the screw assemblies are arranged in parallel to provide a shearing action against one another.
Exemplary of the second common type is U.S. Pat. No. 2,639,898 which discloses a preheater having a rotatable central shaft and a tubular helical coil attached to the shaft. Fluid flows through a portion of the shaft and through the entirety of the singular coil. The shaft can also be partitioned to provide fluid flow throughout the shaft. This patent also discloses in FIG. 8 a dissolver unit having two spaced, rotatable hollow header discs between which extend plural helical tubes of such large pitch that less than a complete turn is encompassed by the tubes. A heating medium flows from one header, through the tubes to the other header, and then to a discharge.
Among some of the other types of processors is that disclosed in U.S. Pat. No. 2,753,159 which includes subassemblies of a single hollow flight permanently mounted on a shaft, with a number of the subassemblies secured between two rotatable drums which drums are also joined by a central shaft. A heat transfer fluid flows through a portion of the shaft to one drum, in parallel through the plural subassemblies to the other drum, and back through a section of the central shaft. Rotation of the central shaft rotates the entire assembly.
Another type of processor is disclosed in U.S. Pat. No. 3,386,708 which includes a plurality of concentric cylinders and concentric hollow or solid helical screws of differing diameters interspersed among the cylinders. The unit can be operated as a conveyor or is stated to be capable of a design which provides no conveying action, but merely a turning of the feed material within a cylinder.
Yet another processor type is disclosed in U.S. Pat. No. 2,153,082 and includes sets of water circulating tubes appearing generally as a part of a helical turn, each extent of each tube receiving or transferring fluid to and from headers within a central shaft from which the tubes extend. Also included is a helical scraper of plural turns extending radially about the length of the central shaft.
Another type of processor, disclosed in U.S. Pat. No. 742,603, includes hollow spaced manifolds each having three identically sized radially extending arms and a plurality of straight tubes extending between the arms of the two manifolds. A heat transfer fluid flows back and forth through the arms and tubes in a prearranged pattern such that the overall fluid flow path is generally described as being of spiral fashion.
Each of the disclosed processors, while useful for its intended purpose, has certain difficiencies for which improvement can be made. This is exemplified by the difficulties associated with the fabrication and repair of each unit. Additionally, high stresses induced during manufacture, particularly in the vicinity of the weldments, often exist among processor components which stresses are intensified under operating conditions and which can eventually lead to failure. It is thus desirable to provide a material processor which alleviates these and other concerns and particularly which is reliable yet easy to repair and maintain in the event of failure.